Method for creating a resistance weld bond between two metals

ABSTRACT

An electrode used for resistance welding is described. In an embodiment, the electrode comprises a two-part construction having an electrode tip portion that is removably contactable to an electrode base. The electrode is constructed such that the respective base and electrode tip portions may be composed of metals having differing melting temperatures, in particular a significant difference in melting temperature of at least 100° C. or more. The electrode is preferably constructed so that the electrode tip portion can be easily removed, thereby leaving the base portion within the fixture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/513,295, filed on Oct. 14, 2014, now U.S. Pat. No. 10,188,245, whichclaims priority from U.S. Provisional application Ser. No. 61/889,603,filed on Oct. 11, 2013.

FIELD OF THE INVENTION

The present invention relates to the art of resistance welding. Morespecifically, the present invention is of a resistance welding electrodehaving a detachable welding electrode tip.

PRIOR ART

The recent rapid development in small-sized electronic devices havingvarious shape and size requirements requires comparably small-sizedelectrochemical cells of different designs that can be easilymanufactured and used in these electronic devices. Preferably, theelectrochemical cell has a high energy density, and one commonly usedcell configuration is a prismatic, case-negative cell design having anintermediate cathode flanked by opposed anode components in contact withthe casing and in electrical association with the cathode.

The diverse variety of materials used in the construction ofelectrochemical cells increases the difficulty of assembling andmanufacturing such small intricate devices. It is desirable to buildsuch electrochemical cells with simplified procedures that create anelectrochemical cell with a durable and robust construction. Suchelectrochemical cells require joining various internal components,composed of differing materials, with a strong durable bond. One ofthese critical connections is that of the terminal pin to the currentcollector. The terminal pin connects the electrochemical cell's internalcurrent collector to a load such as an implantable medical device. U.S.patent application Ser. No. 12/944,859, now U.S. Pat. No. 8,722,238,U.S. Ser. No. 13/867,178, U.S. patent application publications2014/0245600, 2014/0246408 all to Dai et al., and U.S. patentapplication publication 2012/0282519 to Freitag et al., all assigned tothe assignee of the present invention and incorporated by referenceherein, disclose various embodiments and techniques of weldingdissimilar metals for incorporation into an electrochemical cell.

One such welding technique used to join materials, including metalshaving dissimilar melting temperatures, is that of resistance welding inwhich electrical energy is used to generate heat through opposedelectrodes that heat and subsequently fuse materials together. However,because of the diverse materials with their respective distinct materialproperties, since one of the components being joined may have arelatively high melting temperature compared to the other, it issometimes difficult to join and reliably bond such components together.In the case of joining materials with one component having a relativelyhigh melting temperature, an increased amount of electrical energy isgenerally used to increase the amount of resistive heat used to melt theworkpiece.

Specifically, with respect to an electrochemical cell, an increasedamount of electrical energy is generally required to join the terminalpin, typically composed of molybdenum, to that of the current collector,typically composed of aluminum or titanium. In this case, an increasedamount of energy is required to heat the molybdenum and thus enable aweld joint therebetween. However, generating such an increased amount ofenergy to heat the molybdenum terminal pin material generallycauses-excessive wear of the welding electrode and may even cause aportion of the electrode to melt and spall off.

Resistance welding has typically relied upon traditional copperelectrodes 10, 12 having a “uni-body” construction such as thoseillustrated in FIGS. 1A and 1B. As illustrated, the tip and bodyportions of the electrode are of a single uniform construction. The useof such uni-body copper electrodes is generally not ideal when weldingmaterials having at least one material that has a significantlyincreased melting temperature requiring a large amount of energy andheat to join together with another lower melting temperature material.In particular, when welding high melting temperature refractorymaterials, like molybdenum, the high intensity heat that is generatedduring the welding process may cause at least a portion of the copperelectrode tip to melt. In some cases, the melted portion of theelectrode may spall off from the electrode tip and/or splatter onto theweld area. Such melting and splattering of the electrode tip maytherefore leave a residual amount of the electrode material, e.g.copper, on the surface of the workpiece. This residual electrodematerial may therefore not only cause possible cosmetic defects of theweld and surrounding area, but also may negatively affect the strengthand durability of the resultant weld joint. In addition, such residualelectrode materials, such as copper, may adversely affect the chemistryof an electrochemical cell and, thus, potentially negatively affect theperformance of the cell. Therefore, the use of traditional electrodes,such as copper welding electrodes having a uni-body construction, isgenerally not ideal for welding two materials, one with a significantlyhigher melting temperature than the other.

Furthermore, when traditional electrodes of a uni-body constructionbecome worn, the entire electrode must be replaced. This replacement ofthe whole electrode results not only in increased welding costs, butalso increased operational down-time as the manufacturing process isgenerally halted to allow for the installation and alignment of a newelectrode.

The present invention thus provides an improved resistance weldingelectrode design having a two-part construction. More specifically, thepresent invention provides a resistance welding electrode having anelectrode tip portion that is detachable from an electrode base.Therefore, a welding electrode may now be provided that is configured tomore suitably match the melting temperatures and/or the materialcomposition of the workpieces, i.e., the materials to be welded, to thusminimize electrode wear and spalling. In addition, the two-partconstruction of the welding electrode of the present invention allowsfor relatively quick and easy replacement of the electrode tip (theportion that contacts the workpiece) without the added cost anddown-time associated with replacement of the entire welding electrode.

For example, the base may be constructed of a highly electrical andthermal conductive material, such as copper and the electrode tipportion may be constructed from a material with a melting temperaturethat is similar or greater than the melting temperature of theworkpiece. In addition, the electrode tip portion may be composed of amaterial composition that is the same or similar to the workpiece. Thus,excessive electrode tip wear and splatter contamination that may resultfrom a melted electrode tip is minimized.

Furthermore, use of the electrode of the present invention results inminimized welding operational costs. First, the electrode tip of thepresent invention, with its customized materials of construction, ismore wear resistant than traditional electrodes. Second, by providing adetachable electrode tip portion, the tip can easily be replaced, asopposed to replacing the whole electrode when the tip becomes wornthrough normal use. Thus, the design of the resistance welding electrodeof the present invention decreases welding set up time, decreasesoperating down-time and reduces overall welding costs.

SUMMARY OF THE INVENTION

The present invention, therefore, provides an improved resistancewelding electrode having a two-part construction. More specifically, thepresent invention provides a resistance welding electrode having anelectrode tip portion that is detachable from an electrode base portion.

The respective electrode tip and base portions may be constructed of awide range of differing geometrical shapes and materials. Thus, aresistance welding electrode could be custom tailored in both shape andmaterial to weld and join a wide range of differing materials havingdiffering melting temperatures.

In an embodiment, the resistance electrode of the present invention maybe constructed such that the electrode tip portion is placed inremovable physical contact with an exterior surface of the electrodebase portion such that electrical energy readily transfers therebetween.In a more preferred embodiment, the resistance electrode of the presentinvention may be constructed such that the electrode tip portioninterlocks with the respective base portion. In either case, theelectrode tip is designed such that it can be easily removed from thebase.

In an embodiment, the electrode tip portion may be constructed having agroove that preferably resides at least partially within an electrodetip distal end surface. The electrode tip groove, which may beconstructed having a plurality of cross sectional geometrical shapes,helps hold the workpiece in place during the welding process. Inaddition, the electrode tip groove helps concentrate electrical andthermal energy to the workpiece.

Thus, the present invention overcomes many inherent difficulties thatare associated with welding dissimilar materials. In particular, thepresent invention enables the creation of a resistance weld between twomaterials having a wide difference in melting temperatures. Inparticular, the present invention overcomes many inherent difficultiesin the construction of electrochemical cells by facilitating aresistance weld connection between the terminal pin and a wide varietyof metals used for the current collector and having differing meltingtemperatures. Thus, by providing a resistance electrode of a two-partconstruction, manufacturing cost and manufacturing down-time is reducedas only the electrode tip portion is required to be replaced.Furthermore, the present invention enables the utilization of differentcell chemistries that may require the joining of different metals havingan increased difference in melting temperatures that would otherwise notbe possible with a traditional electrode of a uni-body construction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate prior art embodiments of resistance weldingelectrodes having a uni-body construction.

FIGS. 2A and 2B show an embodiment of the resistance welding electrodeof the present invention.

FIGS. 3A-3E illustrates various embodiments of electrode tip portionsthat may be incorporated with the resistance weld electrode of thepresent invention.

FIGS. 4A-4C are cross-sectional views showing various embodiments inwhich the welding electrode base and tip portions may be connected.

FIG. 5 shows an embodiment of a resistance welding setup and fixtureutilizing the resistance welding electrode of the present invention.

FIG. 5A illustrates an alternate embodiment of an electrode tip portionthat may be used with the resistance welding electrode of the presentinvention.

FIG. 6 is a cross-sectional view of an alternative embodiment of awelding fixture which may use the electrode tip portions illustrated inFIGS. 3A-3E and 5A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 2A and 2B, there is shown an embodiment of aresistance welding electrode 20 of the present invention. As shown, theelectrode 20 comprises an electrode base portion 22 and an electrode tipportion 24 that extends outwardly from the base 22. In a preferredembodiment, the electrode tip portion 24 is physically contactable tothe base 22 such that when the tip 24 and the base 22 are in contactwith each other, electrical and thermal energy is readily transferabletherebetween.

The base portion 22 preferably comprises an electrically and thermallyconductive body having a base proximal end 26 that extends alonglongitudinal axis A-A to a base distal end 28. The base proximal end 26is preferably configured to be received within an electrode weldingfixture 30 (FIGS. 5 and 6) and the base distal end 28 is configured tocontact the electrode tip portion 24. As illustrated, a lateral axis B-Bis shown that extends in a perpendicular relationship to longitudinalaxis A-A.

More specifically, the electrode base portion 22 comprises an electrodebase body 32 that extends along longitudinal axis A-A from the electrodebase proximal end 26 having an electrode base proximal end surface 34 tothe electrode base distal end 28 having an electrode base distal endsurface 36. The electrode base distal end surface 36 defines a basedistal end surface area 38. In a preferred embodiment, the respectiveelectrode base proximal and distal end surfaces 34, 36 may extendperpendicularly with respect to longitudinal axis A-A. However, it iscontemplated that either or both of the electrode tip proximal anddistal end surfaces 34, 36 may be oriented at an angular relationshipwith respect to longitudinal axis A-A. For example, either of thesurfaces may be oriented from about 50 to about 60° with respect to axisA-A.

In a preferred embodiment, as illustrated in FIGS. 2A and 2B, the baseportion 22 may be constructed in the form of a cylinder. In theembodiment, the base body 32 comprises a curved exterior base sideway.40 that extends lengthwise along longitudinal axis A-A. The baseproximal and distal ends 26, 28 respectively comprise a curved baseportion diameter 37 that extends perpendicular to longitudinal axis A-A.In a preferred embodiment, the base portion diameter 37 may range fromabout 1 mm to about 100 mm.

Alternatively, the base body 32 may be constructed in a variety ofnon-limiting shapes and sizes. For example, the base body 32 may beconstructed in the form of a plurality of prisms, such as a rectangularprism or a cubic prism. As defined herein a “prism” is a solid bodyhaving two congruent parallel faces, where any cross section parallel tothose faces is congruent to them. A “rectangular prism” is a solidobject that has six faces that are rectangular in shape and a “cubicprism” is a solid object that has six faces that have a squarecross-sectional shape.

As illustrated in FIGS. 2A, 2B and 4A to 4C, the base portion 22comprises a base height 42 that extends parallel to longitudinal axisA-A, a base width 44 (FIG. 4B) that extends perpendicular tolongitudinal axis A-A. In a preferred embodiment, the base height 42 mayrange from about 1 mm to about 200 mm, the base width 44 may range fromabout 1 mm to about 200 mm. In the case where the base portion 22 isconstructed in the form of a prism, such as a rectangular or cubicprism, the base portion 22 has a base depth that ranges from 1 mm toabout 100 mm that extends perpendicular to the base width 44.

Furthermore, the base body 32 may be constructed having a plurality ofnon-limiting cross-sectional shapes that extend perpendicular tolongitudinal axis A-A. Examples of these cross-sectional shapes include,but are not limited to, a rectangle, a square, a triangle, a hexagon, anoctagon, a curved shape or other polygon shapes.

The electrode base portion 22 is preferably composed of an electricallyconductive electrode base first material such as a metal or metallicalloy. Non-limiting examples of electrically conductive base firstmaterials include, but are not limited to, copper, aluminum, stainlesssteel, gold, silver, palladium, and alloys thereof.

In a preferred embodiment, the electrode tip portion 24 comprises anelectrode tip body 48 having an electrode tip proximal end 50 with anelectrode tip proximal end surface 52 (FIGS. 2A and 3A) that extendsalong longitudinal axis A-A to an electrode tip distal end 54 having anelectrode tip distal end surface 56. In a preferred embodiment, therespective electrode tip proximal and distal end surfaces 52, 56 mayextend perpendicularly with respect to longitudinal axis A-A. However,it is contemplated that either or both of the electrode tip proximal anddistal end surfaces 52, 56 may be oriented at an angular relationshipwith respect to longitudinal axis A-A and lateral axis B-B. For example,either of the surfaces may be oriented from about 25° to about 60° withrespect to longitudinal axis A-A and lateral axis B-B.

Similar to the base body 32, the electrode tip body 48 may beconstructed of a plurality of unlimited shapes and sizes as illustratedin FIGS. 2A, 2B and 3A to 3E. In an embodiment shown in FIGS. 2A, 2B and3A to 3D, the electrode tip body 48 may be constructed having opposedfirst and second major sidewalls 58, 60 that extend and meet opposedthird and fourth major sidewalls 62, 64. In a preferred embodiment, asshown in FIGS. 3A to 3D, the opposed first and second major sidewalls58, 60 are positioned about perpendicular to the opposed third andfourth major sidewalls 62, 64. In other words, the electrode tip portion24 may be constructed in the form of a prism such as a rectangular prismor a cubic prism as previously described.

As shown in FIG. 3B, the electrode tip portion 24 comprises an electrodetip height 66 that extends between the proximal and distal electrode tipends 50, 54. The electrode tip portion 24 also comprises an electrodetip width 68 that preferably extends perpendicular to the electrode tipheight 66 and between the third and fourth major side walls 62, 64. Inaddition, the electrode tip portion 24 comprises an electrode tip depth70 that extends perpendicularly between the opposed first and secondsidewalls 58, 60. In a preferred embodiment, the electrode tip height 66may range from about 1 mm to about 200 mm. The electrode tip width 68may range from about 1 mm to about 100 mm and the electrode tip depth 70may range from about 0.5 mm to about 50 mm.

In a preferred embodiment as illustrated in FIGS. 2A, 2B, 3B and 3C, theelectrode tip body 48 may comprise an electrode tip groove 72. Thegroove 72 is designed to hold the workpiece prior to and during welding.In addition, the groove 72 is designed to increase the surface area thatcontacts the workpiece such that heat from the electrode is concentratedat the workpiece. The groove 72 preferably comprises a groove depth 74that penetrates the electrode tip distal end surface 56 and extends atleast partially through the electrode tip height 66.

As shown, the groove 72 preferably comprises a groove length 76 (FIG.3B) that at least partially extends across the electrode tip distal endsurface 56 perpendicular to longitudinal axis A-A. As shown in FIGS. 2A,2B, 3B and 3C, the groove length 76 is preferably oriented aboutperpendicular to the opposed first and second major sidewalls 58, 60.However, it is contemplated that the length 76 of the groove 72 may beoriented such that it extends at an askew orientation with respect toeither the first or second major sidewalls 58, 60. In a preferredembodiment, the groove depth 74 may range from about 0.1 mm to about 10mm or from about 1 percent to about 90 percent of the height 66 of theelectrode tip portion 24. In a preferred embodiment, the electrode tipheight 66 may be constructed to be about 5 times that of the depth 74 ofthe groove 72. Furthermore, the groove length 76 may range from about0.1 mm to about 100 mm or alternatively, from about 5 percent to about100 percent, or about the full span of the depth 70 of the electrode tipportion 24. In addition, the groove 72 comprises a groove width 78 thatranges from about 0.1 mm to about 50 mm. Alternatively, the groove width78 may extend from about 5 percent to about 90 percent of the width 68of the electrode tip portion 24.

In a preferred embodiment, as shown in FIGS. 2A, 2B, and 4A-4C, theelectrode tip groove 72 may comprise a cross-sectional shape orientedperpendicular to longitudinal axis A-A, in the shape of the letter “V”.As shown in this particular example, the groove 72 comprises first andsecond groove sides 80, 82 (FIG. 4A-4C) that extend and meet at a grooveaxis 84 (FIGS. 2A, 2B) that extends perpendicular to longitudinal axisA-A. In a preferred embodiment, each of the first and second groovesides 80, 82 is positioned at an angular orientation from the distal endsurface 56. In a preferred embodiment, either of the first or secondgroove sides 80, 82 may be oriented at an angle that ranges from about20° to about 60° with respect to the electrode tip distal end surface 56and longitudinal axis A-A.

Alternatively, the tip groove 72 may have a curved cross-section thatextends perpendicular to the longitudinal axis A-A within the electrodetip distal end surface 56 and longitudinal axis A-A. In this particularexample, the groove 72 may comprise a groove radius of curvature 85having a point of origin 86 positioned parallel to the electrode tipdistal end surface 56. In a preferred embodiment, the groove radius ofcurvature 85 may range from about 0.1 mm to about 50 mm. Othernon-limiting shapes that the groove cross-section may comprise include arectangle, a square, a triangle, or a hexagon.

FIG. 3A illustrates an example of the electrode tip body 48 in which themajor sidewalls 58, 60, 62, 64 comprise planar surfaces and the firstand second major sidewalls 58, 60 as well as the third and fourth majorsidewalls 62, 64 meet at about 90° with respect to each other. FIG. 3Billustrates an example of the electrode tip body 48 comprising a groove72 having a rectangular cross-section that extends perpendicular tolongitudinal axis A-A. FIG. 3C shows an example of the electrode tipbody 48 with a groove 72 having a curved cross-section. These variouselectrode tip groove 72 embodiments help correctly position theworkpiece while the welding operation is performed. For example, groove72 comprising a rectangular cross-section may be better suited toposition a workpiece having a rectangular cross-section whereas a groove72 having a curved cross-section may be better suited to hold aworkpiece having a curved cross-section.

FIG. 3D illustrates an example of the electrode tip body 48 comprising astep 88 that extends upwardly from the distal end surface 56. In thisparticular embodiment, the step 88 acts as a platform for the workpieceand also acts to concentrate the energy, i.e., thermal and electricalenergy to the workpiece. FIG. 3E illustrates an example of an electrodetip body 48 comprising a cylinder having an electrode tip radius 90.

As previously mentioned and illustrated in FIGS. 2A and 2B, theelectrode tip portion 24 preferably resides at the distal end 28 of thebase portion 22 of the electrode 20. More specifically, the proximal endsurface 52 of the electrode tip portion 24 is electrically contactableto the distal end surface 36 of the electrode base 22 such thatelectrical and thermal energy conducted by the base portion 22 can bereadily transferred to the electrode tip portion 24. Furthermore, theelectrode tip body 48 is physically contactable to the electrode base 22such that it can be easily removed. Thus, by only removing the electrodetip portion 24, and not the whole electrode, as is the case with priorart electrodes 10, 12 such as those illustrated in FIG. 1, from theelectrode base 22, welding process time can be significantly decreased.Since the electrode base portion 22 remains in the welding fixture ,30(FIG. 5), the fixture not need to be opened and closed to allow for theremoval of the worn electrode and the subsequent installment of a newelectrode, as is the case with the prior art electrodes 10, 12comprising a “uni-body” construction. Therefore, when the electrode tipportion 24 of the present invention becomes worn through use, it issimply swapped out for a new electrode tip 24. Furthermore, there is noneed to redress the electrode as is also the case with the prior artelectrodes 10, 12. As used herein “redress” is defined as to sharpenand/or remove melted or partially melted electrode material from theelectrode tip. Prior art resistance electrodes are typically redressedby rubbing a cloth or piece of sand paper against the electrode tip toremove debris and reshape the electrode tip. Therefore, the ability ofthe electrode tip portion 24 to be readily removed from the base portion22 significantly reduces weld processing time. This is especiallyadvantageous when performing a series of repetitive welds. In addition,since only the electrode tip portion 24 is removed, and not the wholeelectrode 10, 12, electrode material costs are significantly reduced.

The electrode tip body 48 is preferably composed of an electricallyconductive electrode tip second material such as a metal or metallicalloy. Non-limiting examples of electrically conductive electrode tipsecond metals include, but are not limited to, copper, aluminum,stainless steel, gold, silver, palladium, and alloys thereof. In apreferred embodiment, the electrode tip portion 24 may be constructed ofa second material having a greater melting temperature than theelectrode base first material. Examples of these electrode tip secondmaterials include but are not limited to molybdenum, tungsten, tantalum,cobalt, nickel, niobium, rhenium and mixtures thereof. Therefore, theelectrode 20 of the present invention may be constructed having the baseportion 22 constructed of copper, which has a relatively high electricaland thermal conductivity, and the separate electrode tip portion 24 maybe composed of a refractory material, such as molybdenum, having amelting temperature that is significantly greater than the meltingtemperature of the electrode base first material. In a preferredembodiment, the electrode tip portion 24 may be constructed of anelectrode tip second metal that comprises a melting temperature that isas much as 200° C. to 1,000° C. or greater than the base electrode firstmetal that comprises the base electrode portion 22. In addition, theelectrode tip second material may be of the same or substantiallysimilar composition, such as an alloy thereof, as the workpiece. In apreferred embodiment, the electrode tip second material may be composedof the same or substantially similar composition as at least one of thefirst and second workpiece metals. In a more preferred embodiment, theelectrode tip second metal may be composed of the same or substantiallysimilar metal as the workpiece metal with the lowest meltingtemperature. As defined herein “workpiece” is the metals intended to bewelded and joined together. A “workpiece metal” is therefore one of theat least two metals that are intended to be welded and joined together.

FIGS. 4A-4C illustrate cross-sectional views of various embodiments inwhich the electrode tip portion 24 is positioned in physical contactwith the electrode base portion 22. As illustrated in FIG. 4A, theelectrode tip portion 24 may be positioned on the electrode base portion22. More specifically, the electrode tip proximal end surface 52 ispositioned in physical contact with the electrode base distal endsurface 36. In a preferred embodiment, the cross-sectional surface areaof the electrode tip proximal end surface 52 may be less than thecross-sectional surface area of the electrode base distal end surface36. Alternatively, the cross-sectional surface area of the electrode tipproximal end surface 52 may be about the same or greater than thecross-sectional surface area of the electrode base distal end surface36.

FIGS. 4B and 4C illustrate embodiments in which the electrode tipportion 24 is mated to the electrode base portion 22. More specifically,as illustrated in FIG. 4B, the electrode tip portion 24 is mated to theelectrode base portion 22 with a ridge and slot feature. As shown, aridge 92 extends outwardly from the electrode tip proximal end surface52 and is configured to mate with a corresponding electrode base slot94. Specifically, as shown, the ridge 92 extends along the electrodeproximal end surface 34 in a perpendicular orientation with respect tolongitudinal axis A-A. In a preferred embodiment, the ridge 92 isdesigned to be received in the corresponding electrode base slot 94 thatextends at least partially within the electrode base distal end surface36. The base slot 94 is preferably dimensioned such that the ridge 92fits therewithin.

Furthermore, illustrated in the embodiment of FIG. 4B, is a terminal pin119 and a tab portion 121 of a current collector of an electrochemicalcell. More specifically, the terminal pin 119 is shown positioned withinthe electrode tip groove 72 and the tab portion 121 is positioned abovethe terminal pin 119. Thus, the electrode tip groove 72 is preferablydimensioned to hold a terminal pin 119 of an electrochemical cell whilea tab portion 121 of a current collector is positioned in contacttherewith.

FIG. 4C illustrates an embodiment in which the electrode tip portionridge 92 further comprises opposed left and right flanges 96A, 96B thatextend outwardly from the respective left and right sides of the ridge92. In a preferred embodiment, these flanges 96A, 96B provide additionalstability that secures the electrode tip portion 24 therewithin whenmated with the base portion 22. To secure the electrode tip portion 24(shown in FIG. 4C) to the base 22, the electrode tip 24 is preferablyslid in a linear direction perpendicularly to longitudinal axis A-A suchthat it securely mates with the base 22. To remove the electrode tipportion, the tip 24 is again slid forwards or backwards perpendicular tolongitudinal axis A-A, until the ridge 92 and/or flanges 96A, 96B becomedisengaged from the base portion slot 94. The embodiment illustrated inFIG. 4C is particularly beneficial when the electrode 20 is positionedin a vertical orientation such as when the electrode comprises the topelectrode in the fixture 30. The flanged portions 96A, 96B of theelectrode tip 92 prevent the tip portion 24 from becoming disengagedfrom the base 22, particularly when the electrode 20 is oriented in anupside-down orientation with the electrode tip distal surface 56pointing in a downward direction towards the ground. It is noted thatwhile the electrode tip 24 of the embodiment shown in FIGS. 2A and 2B isillustrated, the electrode tip portion 24 may comprise either of theelectrode tip portions 24 shown in FIGS. 3A-3E. In a preferredembodiment, the ridge 92 and corresponding base electrode slot 94 inwhich the ridge 92 is received and mates therewithin, may comprise avariety of non-limiting cross-sectional shapes which include, but arenot limited to, a rectangle, a square, a triangle, a pentagon, ahexagon, an oval, a polygon or curved shaped.

FIG. 5 illustrates an embodiment of a welding station 98 that may beused with the electrode 20 of the present invention. As shown, thestation 98 comprises the welding fixture 30 comprising a rod 100 and aclamp 102 that holds the electrode 20 therewithin. In addition, a secondor upper electrode 104, which may or may not comprise the electrode 20of the present invention, is illustrated as positioned above and opposedfrom a first or lower resistance electrode illustrated as the electrode20 of the present invention. In a preferred embodiment, the clamp 102 ofthe welding fixture 30 is designed to hold the base portion 22 of theelectrode 20 within the fixture 30. More specifically, the clamp 102 maybe used to hold the electrode base portion 22 against a fixture wall 106illustrated in FIG. 5.

An electrical power supply 108 is preferably electrically connected tothe electrode 20 of the present invention and the opposed secondelectrode 104. In a preferred embodiment, a positive terminal 110 or anegative terminal 112 of the power source 108 may be electricallyconnected to either the electrode base portion 22 of the electrode ofthe present invention 20 or to the second electrode 104. The other ofthe positive or negative terminals is preferably connected to the otherof the electrode base portion 22 or the second electrode 104.

Alternatively, as illustrated in FIGS. 5 and 5A, the electrode tipportion 24 may comprise an electrode tip bar 114 having an elongated tipbar length 116. A plurality of electrode tip bar grooves 118 preferablyextend at least partially within a distal surface of the electrode tipbar 114. In a preferred embodiment, each of the electrode tip grooves118 defines an electrode tip segment 120. The workpiece to be welded ispreferably positioned within one of the series of grooves 118 thatcomprise the electrode tip bar segment 120.

In a preferred embodiment, the distal end of the second top electrode104 makes contact with the workpiece(s) positioned within the groove 118of the electrode tip bar 114 and a weld connection between theworkpieces is made. As illustrated in the embodiment of FIG. 5, aterminal pin 119 and a tab portion 121 of a current collector of anelectrochemical cell are shown positioned between the upper 104 andlower 20 electrodes. More specifically, the terminal pin 119 isillustrated positioned within the electrode tip bar groove 118 and thetab portion 121 is positioned above and in contact with the terminal pin119. Thus, when the second top electrode 104 and the electrode tip bar114 of the resistive welding electrode 20 of the present invention cometogether, and make contact with the respective terminal lead 119 andcurrent collector tab 121, a weld bond is created therebetween.

Alternatively, the second top resistance welding electrode 104 makescontact with the workpiece positioned in the electrode groove 72 of theelectrode tip portion 24. After the weld connection has been made, theweld tip bar 114 is advanced to an adjacent groove position in anadjacent weld tip bar segment 120 and a second weld is completed. In apreferred embodiment, the electrode tip portion 24 is sequentiallyindexed to each of the groove positions or segments, at which a weldconnection is made. This indexing may be performed manually or bemechanized automatically by a machine. For example, movement of thewelding fixture 30 may be controlled by a machine in which the electrodetip bar is automatically moved to the next position after a certainnumber of welds are made in a segment 120 or after the electrode tip isworn to a specific dimension.

In practice, at least two first and second metals as workpiecescomprising similar or dissimilar melting temperatures are placed betweenthe opposing lower and upper welding electrodes 20, 104 to create a bondtherebetween. In a preferred embodiment, the first and second metals ofthe workpiece may have a difference in melting temperature that isgreater than 125° C., more preferably greater than 250° C. and mostpreferably greater than 500° C. Examples of first workpiece metalsinclude, but are not limited to, aluminum (melting temperature 660° C.),titanium (melting temperature 1,725° C.), nickel (melting temperature1,453° C.), steel (melting temperature 1,130° C.), stainless steel(melting temperature 1,353° C.), niobium (melting temperature 2,468°C.), copper (melting temperature 1,083° C.), gold (melting temperature1,064° C.), silver (melting temperature 961° C.), palladium (meltingtemperature 1,554° C.), and combinations thereof. Examples of secondworkpiece metals include, but are not limited to, molybdenum (meltingtemperature 2,617° C.), tantalum (melting temperature 2,996° C.),tungsten (melting temperature 3,410° C.), and combinations thereof.

In a preferred embodiment, a current is applied to the first and secondworkpiece metals between the top welding electrode 104 and the bottomwelding electrode 20. In a preferred embodiment, a current preferablygreater than 800 amperes is preferably applied to at least the first andsecond workpieces for about one to ten milliseconds. If desired, a forceof between about 10 to about 50 Newtons may also be applied to theworkpieces. In this embodiment, the current is applied between the twowelding electrodes 20, 104 while the force is applied to the top weldingelectrode 104 pressing the workpieces. Alternatively, the force couldalso be applied to the bottom welding electrode 20 pushing upwardstowards the workpieces or applied equally between both weldingelectrodes 20, 104. The application of the current combined with theforce forms a strong bond between the first and second workpieces withina few milliseconds. It is noted however, that while joining twoworkpieces (a first and second workpiece metal) is preferred, anadditional number of metals comprising those discussed in the presentapplication may also be joined together. Additionally, it is noted thatwhile it is preferred that the resistance welding electrode 20 of thepresent invention may be positioned in the lower of the two (lower andupper) opposed welding electrode positions, it is contemplated that theelectrode 20 of the present invention may comprise the upper or bothupper and lower electrode positions in the welding fixture 30.

FIG. 5A illustrates a perspective view of an embodiment of the electrodetip bar 114 illustrated in FIG. 5. As shown, the electrode tip bar 114comprises an elongated length 116 with a rectangular cross section thatextends perpendicular to the length. In addition, a series of discretegrooves 118 extend at least partially within a portion of the distal endsurface perpendicular to its longitudinal length 116. It is furthercontemplated that one or more of the electrode tip portions 24 embodiedin FIGS. 3A-3E may comprise at least one segment 120 of the electrodetip bar 114 illustrated in FIGS. 5 and 5A. As illustrated, a segment 120comprises an electrode tip bar groove 118. In addition, each segment 120is preferably spaced apart from each other.

FIG. 6 illustrates a cross-sectional view of an alternate electrodeembodiment in which the electrode tip bar 114 or electrode tip portion24 is sandwiched between a first electrode base portion 122A and anopposed second electrode base portion 122B. As shown, the electrode bar114 is compressed between the first and second electrode base portions122A, 122B by two opposed electrode fixture rams 100.

Now, it is therefore apparent that the present invention has manyfeatures among which are reduced manufacturing cost and constructioncomplexity. While embodiments of the present invention have beendescribed in detail, that is for illustration, not limitation.

What is claimed is:
 1. A method of creating a resistance weld bondbetween two metals, comprising the steps of: a) providing a firstworkpiece metal; b) providing a second workpiece metal; c) providing anelectrical resistance weld instrument comprising a first resistancewelding electrode and a second resistance welding electrode positionedopposed from the first resistance welding electrode and an electricalpower source electrically connected to the first and second resistancewelding electrodes, wherein either or both of the first and secondresistance welding electrode comprises: i) an electrode base portioncomposed of a first electrically conductive material comprising anelectrode base body having an electrode base proximal end with anelectrode base proximal surface that extends along a longitudinal axisto an electrode base portion distal end with an electrode base distalsurface; ii) an electrode tip portion composed of a second electricallyconductive material comprising an electrode tip body having an electrodetip proximal end with an electrode tip proximal surface that extendsalong the longitudinal axis to an electrode tip distal end with anelectrode distal surface; and iii) wherein the electrode tip portion iscontactable to the electrode base portion so that electrical energy isconductible therebetween; d) placing the first and second workpiecemetals between the opposing first and second resistance weldingelectrodes; and e) applying a current to the first and second resistancewelding electrodes that causes the first workpiece metal and the secondworkpiece metal to join together.
 2. The method of claim 1, includingapplying at least about 1 kA of direct electrical current to the firstand second resistance welding electrodes.
 3. The method of claim 1,including the first workpiece metal having a first melting temperaturethat is at least about 125° C. less than a second melting temperature ofthe second workpiece metal.
 4. The method of claim 1, includingpulsating the electrical current at an interval duration ranging frombetween 10 milliseconds to about 100 milliseconds.
 5. The method ofclaim 1, including selecting the electrode base first material from thegroup consisting of copper, aluminum, stainless steel, gold, silver,palladium, alloys, and mixtures thereof.
 6. The method of claim 1,including selecting the electrode tip second material from the groupconsisting of molybdenum, tungsten, tantalum, cobalt, nickel, niobium,rhenium, and mixtures thereof
 7. The method of claim 1, includingproviding the electrode tip second material with substantially the samematerial composition as either the first or second workpiece materials.8. The method of claim 1, including providing the electrode tip portionwith an electrode tip groove having a groove depth and a groove length,wherein the electrode tip groove depth extends through the electrode tipdistal surface at least partially towards the electrode tip proximal endand the electrode tip groove length extending perpendicular to thelongitudinal axis
 9. The method of claim 8, including providing theelectrode tip groove comprising a cross section shape orientedperpendicular to the longitudinal axis, the shape selected from thegroup consisting of a “V”, a “U”, a rectangle, a square, a hexagon and acurved shape.
 10. The method of claim 1, including providing theelectrode tip portion with an electrode tip ridge having a ridge lengthoriented perpendicular to the longitudinal axis that extends outwardlyfrom the electrode tip proximal surface, the ridge configured to bemateably received within an electrode base slot having an electrode baseslot depth and an electrode base slot length, wherein the electrode baseslot depth extends through the electrode base distal surface at leastpartially towards the electrode base proximal end, the electrode baseslot length extending perpendicular to the longitudinal axis.